Fixed NRF52 compilation error

Config.h

@@ -99,8 +99,6 @@
     #define HAS_PMU false
     #define HAS_NP false
     #define HAS_EEPROM false
-    const int pin_rxen = -1;
-    const int pin_busy = -1;
 
 	#if MCU_VARIANT == MCU_1284P
 		const int pin_cs = 4;
@@ -308,16 +306,17 @@
             #define EEPROM_OFFSET EEPROM_SIZE+0xED000-EEPROM_RESERVED
 
             // following pins are for the sx1262
-            pin_rxen = 37;
+            const int pin_rxen = 37;
             const int pin_reset = 38;
             const int pin_cs = 42;
             const int pin_sclk = 43;
             const int pin_mosi = 44;
             const int pin_miso = 45;
-            pin_busy = 46;
+            const int pin_busy = 46;
             const int pin_dio = 47;
             const int pin_led_rx = LED_BLUE;
             const int pin_led_tx = LED_GREEN;
+            #define RXEN_BUSY_PINS
         #endif
 	#else
 		#error An unsupported board was selected. Cannot compile RNode firmware.
@@ -341,6 +340,11 @@
     #endif
 
 	// MCU independent configuration parameters
+    #ifndef RXEN_BUSY_PINS
+    const int pin_rxen = -1;
+    const int pin_busy = -1;
+    #endif
+
 	const long serial_baudrate  = 115200;
 
 	// SX1276 RSSI offset to get dBm value from